The term "polyoxometalates", as used herein, is a collective term which includes isopolymolybdates, isopolytungstates, and heteropoly species. Certain organoammonium polyoxometalates have found use as catalyst precursors for the ring-opening metathesis polymerization of dicyclopentadiene (DCPD) and other monomers having norbornene structures. U.S. Pat. No. 4,380,617 to Minchak et al. and U.S. Pat. No. 4,426,502 to Minchak describe the use of organoammonium molybdates and tungstates in polymerizing norbornene-type monomers by ring-opening polymerization. These precursors comprise an organoammonium cation in combination with a molybdate or tungstate anion. The disclosed catalysts provide high monomer conversion (greater than 99 percent) when utilized in bulk polymerization processes such as reaction injection molding (RIM). The catalyst will sustain high exotherms, which helps to provide high monomer conversion. The RIM process employs two components: an A component which contains an aluminum alkyl cocatalyst and a B component which contains the organoammonium molybdate or tungstate catalyst component. A significant advance of the disclosed catalyst components over traditional catalysts (WCl.sub.6 and MoCl.sub.5) is that it is less reactive to air and water, and it is less likely to induce prepolymerization of the monomer. These catalyst components are also more soluble in organic solvents, such as the DCPD reactive monomer employed in RIM systems, than traditional catalyst components.
The organoammonium cations derived from the tertiary amines of these precursors, such as tridodecylamine, are good at solubilizing molybdate anions in organic media. However, the large size of some of the anions limits the solubility of the catalyst component in organic media. For example, some of the catalyst components are only slightly soluble in hexane. Improvements are desired to extend the shelf-life of RIM system formulations.
Initial reports of organopolyoxometalates date back to 1908. Syntheses for the organoammonium molybdates are described in U.S. Pat. No. 4,406,840 to Kroenke, which describes tri(tridecyl)ammonium molybdate; U.S. Pat. No. 4,406,839 to Kroenke et al., which describes a process for preparing amine molybdates in a two-phase system; U.S. Pat. No. 4,406,838 to Kroenke, which describes trioctylammonium molybdates; and U.S. Pat. No. 4,406,837 to Kroenke, which describes methyltri(capryl)ammonium molybdates. These amine molybdates are produced by reacting an amine with a molybdate compound in the presence of an acidic aqueous medium. The synthesis of amine molybdates in the presence of an acid salt is described by Kroenke in U.S. Pat. No. 4,217,292. The basic synthesis of organophosphorus and organoarsenic pentamolybdate anions of ligated polyoxometalates, is described by Kwak et al., J. Am. Chem. Soc. (1975) 97, 5735, and Kwak et al., Inorg. Chem. (1976) 15, 9776. Other ligated polymolybdates and polytungstates are described by Liu et al., J. Chem. Ed. (1990), Vol. 67, No. 10. However, these ligated polyoxometalates are not known to be soluble in hydrocarbons.